linux-kernel - Re: [PATCH RFC V2 00/10] perf top optimization

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Date:   Mon, 18 Sep 2017 10:01:00 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     kan.liang@...el.com, peterz@...radead.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org, jolsa@...nel.org,
        namhyung@...nel.org, adrian.hunter@...el.com,
        lukasz.odzioba@...el.com, ak@...ux.intel.com
Subject: Re: [PATCH RFC V2 00/10] perf top optimization

Em Mon, Sep 18, 2017 at 10:57:08AM +0200, Jiri Olsa escreveu:
> On Sun, Sep 10, 2017 at 07:23:13PM -0700, kan.liang@...el.com wrote:
> > From: Kan Liang <kan.liang@...el.com>
> > 
> > The patch series intends to fix the severe performance issue in
> > Knights Landing/Mill, when monitoring in heavy load system.
> > perf top costs a few minutes to show the result, which is
> > unacceptable.
> > With the patch series applied, the latency will reduces to
> > several seconds.
> > 
> > machine__synthesize_threads and perf_top__mmap_read costs most of
> > the perf top time (> 99%).
> 
> looks like this patchset adds locking into code paths
> used by other single threaded tools and that might
> be bad for them as noted by Andi in here:
> 
>   https://marc.info/?l=linux-kernel&m=149031672928989&w=2
> 
> he proposed solution and it was changed&posted by Arnaldo in here:
> 
>   https://marc.info/?l=linux-kernel&m=149132267410294&w=2
> 
> but looks like it never got merged
> 
> could you please add this or similar code before you add the
> locking code/overhead in?

I'm rehashing that patch and adding it on top of what is in my perf/core
branch, will push soon, for now you can take a look at tmp.perf/core.

- Arnaldo